The application relates to a semiconductor device with a semiconductor body and to a method for producing a semiconductor device.
A semiconductor device may include an active region with a vertical drift path of a first conduction type and with a near-surface lateral well of a second, complementary conduction type. In addition, the semiconductor device has an edge region surrounding the active region.
This edge region has a variable lateral doping material zone of the second conduction type, which is also known as a VLD structure (variation of lateral doping zone). This VLD structure or VLD zone adjoins the well. In this type of connection, the concentration of doping material is abruptly reduced from the concentration of the well to the concentration of the VLD structure by approximately 1.5 to 2.5 powers of ten. After this, the variable concentration of doping material is gradually reduced to the drift path concentration along a preset lateral length.
An edge structure of this type provides an improved field distribution in a VLD zone for such semiconductor devices which has been optimised in static terms. This, however, changes drastically during the fast dynamic switching of the semiconductor device. When a power semiconductor device through which a current flows is switched off, the charge carrier plasma in the semiconductor device is degraded by the extraction of holes and electrons, leading to the development of a space charge zone at the anode-side p+-n− junction after a critical period of time.
In particular, when switching with large current rise rates, the concentration of free holes in this space charge zone may become comparable to or even higher than the basic doping of the base zone. This increases the gradient of electric field strength from the drift zone to the complementary-doped well and to the complementary-doped VLD structure, so that the critical electric field strength required for avalanche breakdown can be reached at device voltages which are significantly less than the static breakdown voltage.
To improve semiconductor devices of this type in dynamic terms as well, the robustness of the semiconductor device can be increased by reducing the concentration of free charge carriers in the edge region using known measures. This reduction can for example be achieved by locally reducing the life of the charge carriers, for instance by irradiation with electrons or light ions, in particular protons or helium ions. A further possible method is based on reducing the injection of free charge carriers from the highly doped outer zones in the edge region.
For this purpose, the concentration of the n+-emitter in the edge region is for example reduced in the case of a diode, or the concentration of the p+-collector is reduced in the case of an IGBT. In semiconductor devices with a VLD structure in the edge region it has, however, been found that the critical point in fast dynamic switching lies in the transition region between a complementary-doped well and the VLD zone. At these points—in contrast to the behaviour under static blocking loads—certain hard switching conditions may lead to an excessive field peak far above the critical field strength. This results in a massive generation of additional charge carrier pairs by impact ionization, which are separated by the high electric field.
For these and other reasons, there is a need for the present invention.